By-pass device in variable displacement compressor

ABSTRACT

A by-pass device in a variable displacement compressor has a by-pass passage, a valve body and a deformable separator. The by-pass passage interconnects a discharge pressure region with a crank chamber for releasing refrigerant from the discharge pressure region to the crank chamber. The valve body is arranged in the by-pass passage for opening and closing the by-pass passage. The deformable separator separates a back pressure region from the by-pass passage without sliding. The valve body is urged from a side of an opened position where the valve body is spaced from a valve seat toward a side of a closed position where the valve body contacts with the valve seat by pressure applied from the back pressure region to the separator. The valve body is moved from the closed position to the opened position by deforming the deformable separator.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a by-pass device in a variable displacement compressor.

[0002] In a variable displacement compressor for use in an air conditioner as disclosed in Unexamined Japanese Patent Publication No. 2000-111177, pressure in a drive chamber (a crank chamber in the present application) for accommodating a swash plate is controlled by an electromagnetic control valve. The control valve is operable to open and close a passage interconnecting a discharge chamber, which forms a part of discharge pressure region of the compressor, with the drive chamber. As the control valve opens the passage, refrigerant in the discharge chamber flows into the drive chamber, so that pressure in the drive chamber increases and the inclination angle of the swash plate is reduced, thereby to reduce the displacement of the compressor. As the control valve closes the passage, the refrigerant flowing from the discharge chamber into the drive chamber is blocked, so that the pressure in the drive chamber reduces and the inclination angle of the swash plate is increased, thereby to increase the displacement of the compressor.

[0003] In the variable displacement compressor disclosed in the above Publication, a by-pass device is provided for releasing the refrigerant in the discharge pressure region when the discharge pressure is built up excessively. The discharge pressure region and the drive chamber are also in communication with each other through a passage other than the above-mentioned passage (hereinafter, a by-pass passage) and a control valve (hereinafter, a by-pass valve) other than the above-mentioned control valve is provided in the by-pass passage.

[0004] In the by-pass passage disclosed in the above Publication, the spring force of a spring is applied to a valve body through a differential pressure actuating member and a connector bar. The valve body is urged by the spring force of the spring toward a valve seat. The discharge pressure in the discharge pressure region opposes the suction pressure in a suction pressure region through the differential pressure actuating member. In a state where the total discharge pressure in the discharge pressure chamber applied to the differential pressure actuating member does not exceed the sum of the total suction pressure in the suction pressure region applied to the differential pressure actuating member and the spring force of the spring, the by-pass valve maintains a closed state where the valve body sits on the valve seat. Accordingly, the refrigerant gas in the discharge pressure region does not flow into the drive chamber through the by-pass passage. As the total discharge pressure in the discharge pressure chamber applied to the differential pressure actuating member exceeds the sum of the total suction pressure in the suction pressure region applied to the differential pressure actuating member and the spring force of the spring, the valve body is moved away from the valve seat and the by-pass valve is held in an opened state, accordingly. Thus, the refrigerant in the discharge pressure chamber flows into the drive chamber through the by-pass passage.

[0005] In the above-described by-pass valve, a seal ring need be interposed between the circumferential wall of a partitioned chamber for accommodating the differential pressure actuating member and the peripheral edge portion of the differential pressure actuating member. Lubricating oil is contained in a refrigerant circuit of the air conditioner, and the seal ring is swelled by the lubricating oil. Additionally, the seal ring may be foamed due to fluctuating pressure of the refrigerant. Particularly, in a compressor employing carbon dioxide as the refrigerant, pressure of the refrigerant becomes relatively high and, therefore, the seal ring tends to be easily foamed. When the seal ring is swelled or foamed, sealing performance of the seal ring degrades, with the result that the refrigerant in the discharge pressure chamber leaks through the outer periphery of the pressure differential actuating member into the suction pressure region and, therefore, smooth control of the displacement of a variable displacement compressor fails to be accomplished. Therefore, there is a need for a by-pass device that prevents the leakage of refrigerant.

SUMMARY OF THE INVENTION

[0006] In accordance with the present invention, in a variable displacement compressor which adjusts pressure in a crank chamber in such a manner that refrigerant in a discharge pressure region is introduced into the crank chamber through a supply passage and the refrigerant in the crank chamber is released to a suction pressure region through a bleed passage, displacement of the compressor being controlled by adjusting the pressure in the crank chamber. A by-pass device has a by-pass passage, a valve body and a deformable separator. The by-pass passage interconnects the discharge pressure region with the crank chamber for releasing the refrigerant from the discharge pressure region to the crank chamber. The valve body is arranged in the by-pass passage for opening and closing the by-pass passage. The deformable separator separates a back pressure region from the by-pass passage without sliding. The valve body is urged from a side of an opened position where the valve body is spaced from a valve seat toward a side of a closed position where the valve body contacts with the valve seat by pressure applied from the back pressure region to the separator. The valve body is moved from the closed position to the opened position by deforming the deformable separator.

[0007] Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The features of the present invention that are believed to be novel are set forth with particularity in the appended claims. The invention together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

[0009]FIG. 1 is a longitudinal cross-sectional view of a whole compressor according to a first preferred embodiment of the present invention;

[0010]FIG. 2 is a cross-sectional view that is taken along the line I-I in FIG. 1;

[0011]FIG. 3 is a cross-sectional view that is taken along the line II-II in FIG. 1;

[0012]FIG. 4 is an enlarged schematic view of a by-pass valve in a state where a valve hole is closed according to the first preferred embodiment of the present invention;

[0013]FIG. 5 an enlarged schematic view of the by-pass valve in a state where the valve hole is opened according to the first preferred embodiment of the present invention;

[0014]FIG. 6 is an enlarged schematic view of a by-pass valve according to a second preferred embodiment of the present invention;

[0015]FIG. 7 is an enlarged schematic view of a by-pass valve according to a third preferred embodiment of the present invention;

[0016]FIG. 8A is an enlarged schematic view of a by-pass valve according to a fourth preferred embodiment of the present invention;

[0017]FIG. 8B is a partially enlarged view of the by-pass valve according to the fourth preferred embodiment of the present invention; and

[0018]FIG. 9 is an enlarged schematic view of a by-pass valve according to a fifth preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] A first preferred embodiment of a variable displacement compressor 10 according to the present invention will now be described with reference to FIGS. 1 through 5.

[0020] Referring to FIG. 1, the variable displacement compressor 10 includes a cylinder block 11, a front housing 12 and a rear housing 13. The front housing 12 is connected to the front end of the cylinder block 10. The rear housing 13 is connected to the rear end of the cylinder block 11 through a valve port plate 14, valve forming plates 15, 16 and a retainer plate 17. The cylinder block 11, the front housing 12 and the rear housing 13 cooperate to form a complete housing of the variable displacement compressor 10. A crank chamber 121 is defined by the front housing 12 and the cylinder block 11. A rotary shaft 18 is rotatably supported by the front housing 12 and the cylinder block 11 through radial bearings 25, 26. The front end portion of the rotary shaft 18 protrudes outside the crank chamber 121 and is coupled to a vehicle engine or an external power source E through a pulley (not shown) and a belt (not shown) so as to receive driving force.

[0021] A rotor 19 is fixedly connected to the rotary shaft 18, while a swash plate 20 is supported on the rotary shaft 18 in such a manner that the swash plate 20 is slidable in the axial direction of the rotary shaft 18 and inclinable relative to the rotary shaft 18. As shown in FIG. 2, connecting elements 21, 22 are fixedly connected to the swash plate 20. Guide pins 23, 24 are fixedly connected to the respective connecting elements 21, 22. A pair of guide holes 191, 192 is formed in the rotor 19. The heads of the guide pins 23, 24 are slidably fitted in the respective guide holes 191, 192. The swash plate 20 is slidable in the axial direction of the rotary shaft 18 and rotatable integrally with the rotary shaft 18 because of the linkage between the guide holes 191, 192 and their corresponding guide pins 23, 24. The swash plate 20 is guided for inclination and sliding movement by the linkage between the guide holes 191, 192 and the guide pins 23, 24, and a slidable support of the rotary shaft 18.

[0022] As the radially central portion of the swash plate 20 moves toward the rotor 19, the inclination angle of the swash plate 20 increases. The maximum inclination angle of the swash plate 20 is regulated in such a manner that the swash plate 20 contacts with the rotor 19. The swash plate 20 indicated by the solid line in FIG. 1 is positioned at the maximum inclination angle. As the radially central portion of the swash plate 20 moves toward the side of the cylinder block 11, on the other hand, the inclination angle of the swash plate 20 reduces. The is swash plate 20 indicated by the chain line in FIG. 1 is positioned at the minimum inclination angle.

[0023] A plurality of cylinder bores 111 is formed in the cylinder block 11 for accommodating slidable pistons 28. The rotation of the swash plate 20 is converted to the reciprocation of the pistons 28 through a pair of shoes 29 in a manner well known in the art, so that the pistons 28 reciprocate in the respective cylinder bores 111.

[0024] As shown in FIGS. 1 and 3, a suction chamber 131 and a discharge chamber 132 are defined in the rear housing 13. Suction ports 141 and discharge ports 142 are formed in the valve port plate 14 and the valve forming plates 15, 16. Suction valves 151 are formed in the valve forming plate 15, and discharge valves 161 are formed in the valve forming plate 16, respectively. Gaseous refrigerant in the suction chamber 131, which forms a part of suction pressure region, flows into the cylinder bore 111 through the suction port 141 by pushing away the suction valve 151 as the piston 28 moves in its suction stroke (from right to left as seen in FIG. 1). The gaseous refrigerant compressed in the cylinder bore 111 is discharged into the discharge chamber 132, which forms a part of a discharge pressure region, through the discharge port 142 while pushing away the discharge valve 161 as the piston 28 moves in discharge stroke (from left to right in FIG. 1). The opening degree of the discharge valve 161 is regulated by a retainer 171 formed in the retainer plate 17 with which the discharge valve 161 is brought into contact.

[0025] In the first preferred embodiment, carbon dioxide is employed as the refrigerant.

[0026] As shown in FIG. 1, a thrust bearing 30 is interposed between the rotor 19 and the front housing 12. The thrust bearing 30 receives reactive force of discharge pressure that acts on the rotor 19 through the cylinder bores 111, the pistons 28, the shoes 29, the swash plate 20, the connecting elements 21, 22 and the guide pins 23, 24.

[0027] The rear housing 13 forms a suction passage 31 through which refrigerant gas is introduced into the suction chamber 131 and a discharge passage 32 through which refrigerant gas in the discharge chamber 132 is discharged out of the compressor 10. As shown schematically in FIG. 1, the suction passage 31 and the discharge passage 32 are in communication by an external refrigerant circuit 33. The external refrigerant circuit 33 includes a heat exchanger 34 for removing heat from the refrigerant, an expansion valve 35, and a heat exchanger 36 for transferring ambient heat to the refrigerant. The expansion valve 35 is a thermally automatic expansion valve which is operable to control the flow of refrigerant in response to variation in gas temperature on the outlet side of the heat exchanger 36.

[0028] As shown in FIGS. 1 and 4, the rear housing 13 incorporates a by-pass valve 27 disposed in a by-pass passage 37 which extends from the discharge passage 32 to the crank chamber 121. The by-pass valve 27 includes a cylindrical housing 38, a cylindrical valve seat 39, a diaphragm 40 disposed so as to be movable into contact with or away from the valve seat 39, a spring seat 41 screwed in the cylindrical housing 38 and a return spring 42 interposed between the spring seat 41 and the diaphragm 40 to serve as an urging means. The elastically deformable diaphragm 40 has a peripheral portion which is held by and between the housing 38 and the valve seat 39.

[0029] The valve seat 39 forms a valve hole 391 in the end wall thereof and an outlet 392 at a part of the inner peripheral wall thereof. The valve hole 391 and the outlet 392 communicate with an internal passage 393 of the cylindrical valve seat 39. The valve hole 391, the internal passage 393 and the outlet 392 form a part of the by-pass passage 37.

[0030] The diaphragm 40 is formed at the central portion thereof with a semi-spherical convex portion 401 bulged toward the internal passage 393. The convex portion 401 is selectively located at the closed position where the convex portion 401 is placed in contact with the valve seat 39, thereby to close the valve hole 391 and at the opened position where the convex portion 401 is placed away from the valve seat 39, thereby to open the valve hole 391. The return spring 42 accommodated in a space inside the housing 38 (hereinafter, a back pressure chamber 381) acts on the diaphragm 40 such that the convex portion 401 of the diaphragm 40 is urged from the opened position to the closed position.

[0031] The housing 38 and the valve seat 39 hold fluid-tightly therebetween the peripheral portion of the diaphragm 40 to shut off fluid communication between the internal passage 393 and the back pressure chamber 381 so that the refrigerant gas in the internal passage 393 which forms a part of the by-pass passage 37 does not flow into the back pressure chamber 381 through the peripheral portion of the diaphragm 40. The diaphragm 40 serves as an elastically deformable separator for separating the back pressure chamber 381 from the by-pass passage 37 without sliding. The convex portion 401 which is a part of the diaphragm 40 serves as a valve body for opening and closing the valve hole 391 which forms a part of the by-pass passage 37. In a state where the convex portion 401 closes the valve hole 391, the diaphragm 40 contacts with the valve seat 39 without any substantial deformation. In other words, the diaphragm 40 is pressed against the valve seat 39 by the atmospheric pressure applied to the diaphragm 40 from the back pressure chamber 381 and the spring force of the return spring 42.

[0032] When the convex portion 401 is located in the closed position to contact with the valve seat 39, the inside of the valve hole 391 communicates with the discharge passage 32 which forms a part of the discharge pressure region, so that the inside of the valve hole 391 then also forms a part of the discharge pressure region. In this closing position of the convex portion 401 of the diaphragm 40, the internal passage 393 communicates with the crank chamber 121 through the outlet 392, so that pressure in the internal passage 393 is substantially equivalent to the pressure in the crank chamber 121 (crank pressure).

[0033] The back pressure chamber 381 accommodating the return spring 42 communicates with an atmospheric region through a vent 411 which is formed in the end wall of the spring seat 41. Accordingly, the back pressure chamber 381 is a part of the atmospheric region. Pressure resulting from the spring force of the return spring 42 and the atmospheric pressure is applied from the back pressure chamber 381 that is a part of back pressure region to the diaphragm 40 that serves as the separator. That is, the spring force of the return spring 42 and the atmospheric pressure work in opposition through the diaphragm 40 to the pressure in the internal passage 393 and pressure in the valve hole 391 (the discharge pressure).

[0034] As shown in FIG. 1, the discharge chamber 132 and the crank chamber 121 are in communication through a supply passage 43. Also, the crank chamber 121 and the suction chamber 131 communicate with each other through a bleed passage 44. The refrigerant in the crank chamber 121 flows to the suction chamber 131 through the bleed passage 44.

[0035] An electromagnetic control valve 45 is provided in the supply passage 43. The control valve 45 receives energization/de-energization control of a controller C. The controller C is activated by turning on air conditioner switch 46 and connected to a temperature setting device 47 for setting a desired target compartment temperature and an actual temperature detector 48 for detecting the current compartment temperature. The controller C is operable to energize or de-energize the control valve 45 based on the information of the target temperature set by the temperature setting device 47 and the current temperature detected by the actual temperature detector 48.

[0036] In the de-energized state, the control valve 45 is closed, thereby to block the flow of refrigerant from the discharge chamber 132 to the crank chamber 121 through the supply passage 43. Since the refrigerant in the crank chamber 121 flows to the suction chamber 131 through the bleed passage 44, the pressure in the crank chamber 121 reduces. Accordingly, the inclination angle of the swash plate 20 increases to increase the displacement of the compressor 10. In the energized state, the control valve 45 is opened, thereby to allow the flow of refrigerant from the discharge chamber 132 to the crank chamber 121 through the supply passage 43. Accordingly, the pressure in the crank chamber 121 increases, so that the inclination angle of the swash plate 20 is reduced, thereby to reduce the displacement of the compressor 10.

[0037] When the sum of the total pressure in the discharge passage (or discharge pressure) and the total pressure in the crank chamber 121 (or crank pressure) both prevailing on one side of the diaphragm 40 is not greater than the sum of the atmospheric pressure and the force of the return spring 42 acting on the diaphragm 40 from the opposite side, the convex portion 401 of the diaphragm 40 is held in the solid-line position of FIG. 4 to close the by-pass passage 37, thereby to prevent a flow of refrigerant gas in the discharge passage 32 to the crank chamber 121 through the by-pass passage 37.

[0038] On the other hand, when the sum of the total pressure in the discharge passage and the total pressure in the crank chamber 121 exceeds the sum of the atmospheric pressure and the force of the return spring 42, the convex portion 401 of the diaphragm 40 is elastically deformed as shown by dash-line of FIG. 4 to open the by-pass passage 37 with the result that the refrigerant gas in the discharge passage 32 flows into the crank chamber 121 through the by-pass passage 37. In other words, when the pressure in the discharge pressure region excessively increases, part of the refrigerant in the discharge pressure region is released to the crank chamber 121 through the by-pass passage 37. As the refrigerant in the discharge pressure region is released to the crank chamber 121 through the by-pass passage 37, the pressure in the crank chamber 121 increases, so that the inclination angle of the swash plate 20 reduces. Accordingly, the displacement of the compressor 10 reduces, and the discharge pressure reduces. As the discharge pressure reduces, the diaphragm 40 contacts with the valve seat 39 to close the by-pass passage 37.

[0039] According to the first preferred embodiment of the present invention, the following advantageous effects are obtained.

[0040] (1-1) The diaphragm 40 which serves as the separator elastically deforms to open and close the by-pass passage 37, while the diaphragm 40 regularly separates the back pressure chamber or the back pressure region 381 from the by-pass passage 37 without sliding on a contact target, such as the housing 38 and the valve seat 39. Accordingly, the refrigerant in the by-pass passage 37 does not leak into the back pressure chamber 381.

[0041] (1-2) There is a possibility that the pressure in the discharge pressure region excessively increases to an abnormal level, and pressure differential between the discharge pressure region and the back pressure chamber 381 excessively increases to an abnormal level, accordingly. In this case, the strength of the separator is set in such a manner that the separator is broken by the abnormal pressure differential, so that the abnormal pressure in the discharge pressure region is released due to the breakage of the separator. FIG. 5 shows a state where the diaphragm 40 has been broken as a result of an abnormal increase in the pressure in the discharge pressure region. As the diaphragm 40 breaks, part of the refrigerant in the discharge passage 32 which forms part of the discharge pressure region is released to the back pressure chamber 381. If the back pressure chamber 381 communicates with the suction chamber 131, the abnormally high pressure in the discharge pressure region does not rapidly reduce. Since the back pressure chamber 381 is a part of the atmospheric region in the first preferred embodiment, the abnormally high pressure in the discharge pressure region rapidly reduces. Namely, in view of the need of rapidly reducing the abnormally high pressure in the discharge pressure region, it should be so arranged that the back pressure chamber 381 is a part of the atmospheric region.

[0042] (1-3) The length of the return spring 42 in the direction in it expands and contracts, that is, the longitudinal length of the return spring 42, is varied by changing the position where the spring seat 41 is screwed relative to the housing 38. That is, the longitudinal length of the return spring 42 in a normal state where the diaphragm 40 contacts with the valve seat 39 is adjustable. As the longitudinal length of the return spring 42 is shortened, the spring force of the return spring 42 strengthens. As the longitudinal length of the return spring 42 is lengthened, the spring force of the return spring 42 weakens. The housing 38 and the spring seat 41 which are screwed relative to each other serve as an urging force adjustor for adjusting the spring force (or urging force) of the return spring or an urging means 42.

[0043] The valve hole 391 may be closed by elastically deforming the diaphragm 40 without utilizing the return spring 42. However, it is difficult to appropriately adjust the pressure in the discharge pressure region only by elastically deforming the diaphragm 40 when the refrigerant in the discharge pressure region is released to the crank chamber 121 through the by-pass passage 37.

[0044] With respect to the urging force adjustor in the first preferred embodiment, the spring force of the return spring 42 is appropriately adjusted by changing the position where the spring seat 41 is screwed relative to the housing 38. That is, the urging force adjustor in the first preferred embodiment is effective to appropriately set the pressure in the discharge pressure region when the refrigerant in the discharge pressure region is released to the crank chamber 121 through the by-pass passage 37.

[0045] Incidentally, the position to screw the spring seat 41 may be changed, for example, in such a manner that the vent 411 forms a square hole and the spring seat 41 is rotated by a wrench that fits the square hole.

[0046] (1-4) In a state where the diaphragm 40 closes the valve hole 391, the pressure in the discharge pressure region is only applied from the side of the valve hole 391 to the central portion (the convex portion 401) of the diaphragm 40. The pressure in the crank chamber 121 (the crank pressure) is applied to the peripheral portion of the diaphragm 40. That is, the pressure sensing area of the diaphragm 40 for the discharge pressure is much smaller than that for the crank pressure. When the pressure sensing portion of the diaphragm 40 for the crank pressure is provided around the pressure sensing portion of the diaphragm 40 for the discharge pressure, the pressure sensing area of the diaphragm 40 for the discharge pressure may be made smaller. As a result, the total discharge pressure applied to the diaphragm 40, which is higher than the crank pressure, may be reduced. If the total discharge pressure applied to the diaphragm 40 is thus reduced, the pressure sensing area of the diaphragm 40 for the atmospheric pressure on the side of the back pressure chamber 381 may be reduced or the return spring 42 may be made smaller. That is, the arrangement of the diaphragm 40 in which the pressure sensing portion thereof for the crank pressure is provided around the pressure sensing portion for the discharge pressure contributes to the compactness of the by-pass valve 27.

[0047] (1-5) With respect to the diaphragm 40 having the convex portion 401 as the valve body, the convex portion 401 of the diaphragm 40 is easily formed by press working.

[0048] A second preferred embodiment of the present invention will now be described with reference to FIG. 6. The same reference numerals denote the substantially identical components to those of the first preferred embodiment.

[0049] With respect to a by-pass valve 27A of the second preferred embodiment, in a state where the convex portion 401 of the diaphragm 40 closes the valve hole 391, pressure in the valve hole 391 is substantially equivalent to the pressure in the crank chamber 121 (the crank pressure). An inlet 394 is formed in the circumferential wall of the valve seat 39 and communicates with the discharge passage 32. The inlet 394, the internal passage 393 and the valve hole 391 form a part of the by-pass passage 37.

[0050] In a state where the convex portion 401 of the diaphragm 40 closes the valve hole 391, the pressure in the crank chamber 121 (the crank pressure) is only applied from the side of the valve hole 391 to the central portion of the diaphragm 40. The pressure in the discharge pressure region is applied to the peripheral portion of the diaphragm 40.

[0051] According to the second preferred embodiment, the same advantageous effects as those mentioned in the above-mentioned paragraphs (1-1) through is (1-3) and (1-5) for the first preferred embodiment are obtained.

[0052] A third preferred embodiment of the present invention will now be described with reference to FIG. 7. The same reference numerals denote the substantially identical components to those of the first preferred embodiment.

[0053] With respect to a by-pass valve 27B of the third preferred embodiment, a ball-shaped valve body 49 is connected to a diaphragm 40B for opening and closing the valve hole 391. The valve body 49 receives the spring force of the return spring 42 through the diaphragm 40B. The return spring 42 urges the valve body 49 in the direction to close the valve hole 391.

[0054] According to the third preferred embodiment in which the diaphragm 40B and the valve body 49 are separately provided, the same advantageous effects as those mentioned in the above-mentioned paragraphs (1-1) through (1-4) are obtained.

[0055] A fourth preferred embodiment of the present invention will now be described with reference to FIGS. 8A and 8B. The same reference numerals denote the substantially identical components to those of the first preferred embodiment.

[0056] The structure of a by-pass valve 27C in the fourth preferred embodiment will be described. The by-pass valve 27C includes a cylindrical housing 51 which is screwed into a cylindrical support cylinder 50 which is in turn secured to the rear housing 13. The by-pass valve 27C further includes a support seat 52 secured in the cylinder of the housing 51 and a bellows 53 connected to the support seat 52. A valve body 54 is secured to the outer surface of an end portion 531 of the bellows 53. The bellows 53 accommodates a guide rod 55 and a return spring as an urging means 56. The return spring 56 is interposed between the support seat 52 and a head 551 of the guide rod 55. A vent 521 is formed in the support seat 52, and the guide rod 55 is inserted into the vent 521. Another vent 511 is formed in the end wall of the housing 51 for communication with a region (a back pressure chamber 532) in the bellows 53 through the vent 521.

[0057] A valve seat 57 is screwed into the cylinder of the housing 51. A valve hole 571 is formed in the valve seat 57 for communication with the discharge passage 32 through the inside of the support cylinder 50. An outlet 58 is formed through the circumferential wall of the support cylinder 50 and the circumferential wall of the housing 51. The outlet 58 and the valve hole 571 communicate with an internal passage 512 in the cylinder of the housing 51. The valve hole 571, the internal passage 512 and the outlet 58 form part of the by-pass passage 37.

[0058] The return spring 56 accommodated in the back pressure chamber 532 urges the valve body 54 toward the valve seat 57 through the head 551 of the guide rod 55 and the end portion 531 of the bellows 53. The valve hole 571 is opened and closed by the valve body 54. That is, the valve body 54 opens and closes the by-pass passage 37.

[0059] The bellows 53 and the valve body 54 separate the internal passage 512 from the back pressure chamber 532 so that the refrigerant in the internal passage 512 which is a part of the by-pass passage does not flow into the back pressure chamber 532. The bellows 53 and the valve body 54 serve as an elastically deformable separator for separating the back pressure chamber 532 from the by-pass passage 37 without sliding. The valve body 54 is pressed against the valve seat 57 by the atmospheric pressure applied from the back pressure chamber 381 to the end portion 531 of the bellows 53 and the spring force of the return spring 56.

[0060] When the valve body 54 is located at a closed position to contact with the valve seat 57, the inside of the valve hole 571 communicates with the discharge passage 32, so that the inside of the valve hole 571 then forms a part of the discharge pressure region. In the above closing position of the valve body 54, the inside of the internal passage 512 communicates with the crank chamber 121 through the outlet 58, so that the pressure in the inside of the internal passage 512 is substantially equivalent to the pressure in the crank chamber 121 (the crank pressure).

[0061] The back pressure chamber 532 communicates with the atmospheric region through the vents 521, 511. Accordingly, the back pressure chamber 532 is a part of the atmospheric region, so that the spring force of the return spring 56 and the atmospheric pressure act as the pressure applied from the back pressure chamber or the back pressure region 532 to the end portion 531 of the bellows 53. That is, the spring force of the return spring 56 and the atmospheric pressure act in opposition to the pressure in the internal passage 512 and pressure in the valve hole 571 (the discharge pressure) through the bellows 53.

[0062] The sum of the total discharge pressure in the valve hole 57 applied to the valve body 54 in the direction in which the valve body 54 is separated from the valve seat 57 and the total crank pressure in the internal passage 512 both applied to the valve body 54 in the direction in which the valve body 54 is moved away from the valve seat 57 is referred to as F1. The total atmospheric pressure in the back pressure chamber 532 applied to the valve body 54 in the direction in which the valve body 54 is urged toward the valve body 57 and the pressure resulting from the spring force of the return spring 56 is referred to as F2. Where F1 is lower than F2, the valve body 54 is held at the closed position, as shown in FIG. 8A. In this position, the by-pass passage 37 is closed, so that the refrigerant in the discharge passage 32 does not flow into the crank chamber 121 through the by-pass passage 37.

[0063] Where F1 exceeds F2, the bellows 53 elastically deforms to move the valve body 54 away from the valve seat 57 at an opened position. Accordingly, the by-pass passage 37 is opened, so that the refrigerant in the discharge passage 32 flows into the crank chamber 121 through the by-pass passage 37. That is, when the pressure in the discharge pressure region excessively increases, the refrigerant in the discharge pressure region is released to the crank chamber 121 through the by-pass passage 37. As the refrigerant in the discharge pressure region is released to the crank chamber 121 through the by-pass passage 37, the pressure in the crank chamber 121 increases and the inclination angle of the swash plate 20 reduces, accordingly. Thus, the displacement of the compressor 10 reduces, and the discharge pressure is reduced. With such a reduction of the discharge pressure, the valve body 54 is brought into contact with the valve seat 57, thereby to close the by-pass passage 37.

[0064] According to the fourth preferred embodiment, the following advantageous effects are obtained.

[0065] (4-1) The bellows 53 and the valve body 54 which serve as the separator open and close the by-pass passage 37, while normally separating the back pressure chamber or the back pressure region 532 from the by-pass passage 37 without sliding on the contact target, such as the support seat 52 and the valve seat 57. In this case, only the bellows 53 elastically deforms. Accordingly, the refrigerant in the by-pass passage 37 does not leak into the back pressure chamber 532.

[0066] (4-2) There is a possibility that the pressure in the discharge pressure region excessively increases to an abnormal level so that the pressure differential between the discharge pressure region and the back pressure chamber 532 excessively increases to an abnormal level. In such a state, the strength of the bellows 53 is set in such a manner that the bellows 53 is broken by the abnormal pressure differential, so that the abnormal pressure in the discharge pressure region is released due to the breakage of the bellows 53. As the bellows 53 is thus broken, part of the refrigerant in the discharge passage 32 which is a part of the discharge pressure region is released to the back pressure chamber 532. Since the back pressure chamber 532 is a part of the atmospheric region, the abnormally high pressure in the discharge pressure region rapidly reduces. Namely, in view of the need of rapidly reducing the abnormally high pressure in the discharge pressure region, it should be so arranged that the back pressure chamber 532 desirably forms a part of the atmospheric region.

[0067] (4-3) As the position where the valve seat 57 is screwed relative to the housing 51 is changed, the length of the return spring 56 in the direction in which it expands and contracts, that is, the longitudinal length of the return spring 56, is varied. This means that the longitudinal length of the return spring 56 in a normal state where the valve body 54 contacts with the valve seat 57 is adjustable. That is, the urging force of the return spring 56 is increased as the longitudinal length of the spring 56 is reduced, while the urging force is reduced with an increase of the longitudinal length of the spring 56. The housing 51 and the valve seat 57 which are screwed relative to each other serve as an urging force adjustor for adjusting the spring force (or urging force) of the return spring as an urging means 56.

[0068] The valve hole 571 may be closed by elastically deforming the bellows 53 without utilizing the return spring 56. However, it is difficult to adjust appropriately the pressure in the discharge pressure region only by elastically deforming the bellows 53 when the refrigerant in the discharge pressure region is released to the crank chamber 121 through the by-pass passage 37.

[0069] With respect to the urging force adjustor in the fourth preferred embodiment, the spring force of the return spring 56 is appropriately adjusted only by changing the position where the valve seat 57 is screwed relative to the housing 51. That is, the urging force adjustor in the fourth preferred embodiment is effective to appropriately set the pressure in the discharge pressure region when the refrigerant in the discharge pressure region is released to the crank chamber 121 through the by-pass passage 37.

[0070] Incidentally, the position to screw the valve seat 57 may be changed, for example, in such a manner that the valve hole 571 partially forms a square hole and the spring seat 41 is rotated by a wrench that fits the square hole.

[0071] (4-4) The pressure sensing area of the valve body 54 for the discharge pressure is much smaller than that for the crank pressure. When the pressure sensing portion of the valve body 54 for the crank pressure is provided around the pressure sensing portion of the valve body 54 for the discharge pressure, the pressure sensing area of the valve body 54 for the discharge pressure may be made smaller. As a result, the total discharge pressure which is higher than the crank pressure and applied to the valve body 54 may be reduced. If the total discharge pressure applied to the valve body 54 is thus reduced, the pressure sensing area of the valve body 54 for the atmospheric pressure on the side of the back pressure chamber 532 may be reduced, thus contributing to the compactness of the return spring 56. That is, when the pressure sensing portion of the valve body 54 for the crank pressure is provided around the pressure sensing portion of the valve body 54 for the discharge pressure, it contributes to the compactness of the by-pass valve 27C.

[0072] A fifth preferred embodiment of the present invention will now be described with reference to FIG. 9. The same reference numerals denote the substantially identical components to those of the fourth preferred embodiment.

[0073] With respect to a by-pass valve 27D in the fifth preferred embodiment, a valve seat 57D is integrally formed with a cylindrical housing 51D. The valve hole 571 is formed in the valve seat 57D. The support seat 52 is slidably fitted in the cylinder of the housing 51D. A screw body 59 is screwed into the cylinder of the housing 51D. The support seat 52 is pressed to contact with the screw body 59 by the spring force of the return spring 56. A vent 591 is formed in the screw body 59. The back pressure chamber 532 in the bellows 53 communicates with the atmospheric region through the vents 521, 591.

[0074] According to the fifth preferred embodiment, the same advantageous effects as those mentioned in the above-mentioned paragraphs (4-1), (4-2) and (4-4) of the fourth preferred embodiment and the following advantageous effects are obtained.

[0075] As the position of the screw body 59 relative to the housing 51D is changed, the length of the return spring 56 in the direction in which it expands and contracts, that is, the longitudinal length of the return spring 56, may be varied. The housing 51D and the screw body 59 which are screwed relative to each other serve as the urging force adjustor for adjusting the spring force of the return spring as an urging means 56. With the urging force adjustor in the fifth preferred embodiment, the spring force of the return spring 56 is appropriately adjusted merely by changing the position of the screw body 59 relative to the housing 51D.

[0076] Incidentally, the position to screw the screw body 59 may be changed, for example, in such a manner that the vent 591 partially forms a square hole and the valve seat 57 is rotated by utilizing the wrench that fits the square hole.

[0077] The present invention is not limited to the embodiments described above but may be modified into the following alternative embodiments.

[0078] (1) In an alternative embodiment to the fourth and fifth preferred embodiments, in a state where the valve body 54 closes the valve hole 571, the valve hole 571 forms a part of the crank pressure region, while the internal passage 512 forms a part of the discharge pressure region.

[0079] (2) In an alternative embodiment to the fourth and fifth preferred embodiments, the end portion 531 of the bellows 53 serves as a valve body. Namely, the end portion 531 is brought into contact with and moved away from the valve seat, thereby to open and close the valve hole 571.

[0080] Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein but may be modified within the scope of the appended claims. 

What is claimed is:
 1. A by-pass device in a variable displacement compressor which adjusts pressure in a crank chamber in such a manner that refrigerant in a discharge pressure region is introduced into the crank chamber through a supply passage and the refrigerant in the crank chamber is released to a suction pressure region through a bleed passage, displacement of the compressor being controlled by adjusting the pressure in the crank chamber, the by-pass device comprising: a by-pass passage interconnecting the discharge pressure region with the crank chamber for releasing the refrigerant from the discharge pressure region to the crank chamber; a valve body arranged in the by-pass passage for opening and closing the by-pass passage; and a deformable separator separating a back pressure region from the by-pass passage without sliding, wherein the valve body is urged from a side of an opened position toward a side of a closed position, the valve body being spaced from a valve seat at the opened position, the valve body contacting with the valve seat by pressure applied from the back pressure region to the separator, the valve body being moved from the closed position to the opened position by deforming the separator.
 2. The by-pass device according to claim 1, wherein the deformable separator is set to be broken when pressure differential between the discharge pressure region and the back pressure region increases to an abnormal level.
 3. The by-pass device according to claim 1, wherein the back pressure region is a part of atmospheric region.
 4. The by-pass device according to claim 1, further comprising: an urging means for elastically urging the deformable separator from the side of the back pressure region so as to urge the valve body from the side of the opened position toward the side of the closed position; and an urging force adjustor for adjusting urging force of the urging means.
 5. The by-pass device according to claim 4, wherein the urging means is a spring, the urging force adjustor is a screw member which serves as a spring seat for the spring, a position where the screw member is screwed being changed to vary spring force of the spring.
 6. The by-pass device according to claim 1, wherein the deformable separator is a diaphragm.
 7. The by-pass device according to claim 6, wherein the diaphragm includes a convex portion as the valve body for opening and closing a valve hole.
 8. The by-pass device according to claim 6, wherein the valve body forms a ball shape, the valve body being connected to the diaphragm.
 9. The by-pass device according to claim 1, wherein the deformable separator is a bellows.
 10. The by-pass device according to claim 1, wherein the pressure in the discharge pressure region is applied to a central portion of the valve body, the pressure in the crank chamber being applied to a peripheral portion of the valve body.
 11. The by-pass device according to claim 1, wherein the deformable separator elastically deforms to move the valve body from the closed position to the opened position. 